Excentric motion translating apparatus

ABSTRACT

A translation element, a so-called driving dog or transmitter, for translating the rotation of the center of gravity of an excentrically mounted excentric gear wheel (9) to a first shaft (14) when said wheel simultaneously executes a planetary movement about a second shaft. A rigid body (10,25) which is pivotably mounted about first pins (11, 12) has axially directed, tooth-like projections (26, 27) fitting with negligible play into two radially counter-directed apertures (22, 23) in said wheel (9) for permittinhg said projections to execute a radial reciprocally gliding motion in the apertures, simultaneously as they execute a rolling motion in said apertures, while the rigid body pivots about the first pins. A sleeve (245) is used to translate the rotation of a first shaft to a second shaft, said shafts not needing to be coaxial, parallel or needing to have a constant mutual, axial spacing, said sleeve co-acting with pins and projections which are in force-transmitting communication with each other and are arranged on the sleeve and on either of the shafts.

The present invention relates to a new movement translation element, aso-called transmitter or driving dog, the primary task of which is totranslate the rotation of the excentrically mounted excentric gear wheelin an excentric gear to the output shaft thereof. Another application isas a coupling between shafts, particularly within the art of servosystems, and where the coupling does not transmit a bending movement.

A gear of the kind mentioned has an excentric gear wheel, also known asa satellite wheel or planet wheel, which is freely mounted on anexcentric stub shaft which rotates together with the input shaft of thegear. The excentric gear wheel is in mesh with an outer, stationary,fixed gear wheel and rolls over the internal teeth thereof. Thecircumference of the excentric gear wheel is somewhat less than that ofthe fixed gear wheel. As it runs over the internal teeth of the fixedgear wheel, the excentric wheel executes slow rotation about itsmounting on the excentric shaft simultaneously as its centre of gravityrotates at a high rotational rate about the input shaft. The HarmonicDrive ® gear is not counted as an excentric gear. Neither are planetgears or differential gears where the translation of rotation takesplace with gear wheels to the output shaft. With regard to theproperties of these gear types I refer to the description in myinternational patent application with the title "Excentric Gear" withthe number 87 00291-1.

It is known to use a lever system or two slides, which are mutuallydisplaced 90° (see Swedish patent 342 875) to translate the slowrotation of the excentric wheel to the output shaft.

These known transmission mechanisms are complicated and voluminous. Theyalso have large backlash when the direction of rotation of the inputshaft is reversed. Transmission means of this kind are used in such asships, where such backlash can be tolerated and where there are norestrictions on space. In connection with ships, it is thus known toutilize pins as translation means, where the pins engage in holes in theexcentric gear wheel. Two excentric wheels are used with theexcentricity displaced by 180°, so that the gear will not have backlashdue to the necessary diameter difference between the pins or rollers andthe holes.

This well-known and often used principle has several seriousdisadvantages:

(a) Each roller is activated as force transmitter under a given angle ofeach completed revolution of the input shaft. The radial distance to thecentre of the excentric wheel from the force transmitting roller variesas this angle is passed through. (The excentricity direction sweeps withthe rotational rate of the input shaft past each roller). This radialvariation in distance causes a sinus-shaped pulsation to be superposedon the rotational rate of the output shaft. In other words, the geardoes not transmit a true angle. This pulsation can be reduced, but noteliminated, by using a large number of pins and rollers.

(b) Very tight tolerances on the ingoing components are required to getthe gear to be free from backlash.

(c) Each roller must momentarily transmit the major part of the outputshaft torque. A large reaction force then loads the output shaftbearing.

(d) The structure is complicated. The principle is difficult to use forsmall servo gears.

(e) The gear is noisy.

Another principle for translating the rotation of the excentric gearwheel to the output shaft is to use two universal joints. Thedisadvantage is that the structure is voluminous axially. Using oneuniversal joint allowing axial movements in each direction istheoretically conceivable.

It is also known to utilize an elastic ruber connection between drivingdog pins, which are arranged on the output shaft, and holes which aresituted in the excentric wheel.

The present invention relates to a translation element of the kinddescribed in the introduction, which does not have the disadvantages ofthe previously mentioned structures with regard to complexity, largevolume, play, high noise level and untrue angle translation.

The driving dog proposed in accordance with the invention has a shortaxial length.

The driving dog in accordance with the invention allows the output shaftto form an angle relative to the input shaft, and also to execute acertain restricted axial movement. By mounting the output shaft in anangularly adjustable bearing, e.g. a ball bearing or spherical planebearing, the gear can be one of the two bearings by which a shaft isjournalled at its both ends, whereby the bearings adjust themselveswithout stresses, i.e. no bending forces are taken up in the bearings.

Different embodiments of the invention will now be described in moredetail in connection with the accompanying drawings, where

FIG. 1 is a front view of a known movement translating means,

FIG. 2 is a longitudinal cross section of the means in FIG. 1,

FIG. 3 is an exploded view of a first embodiment of a driving dog inaccordance with the present invention, the driving dog being included ina excentric gear,

FIG. 4 is view of the excentric gear wheel,

FIG. 5 is a front view of a driving dog,

FIG. 6 is a side view of the driving dog illustrated in FIG. 5,

FIG. 7 is view along the line VII--VII in FIG. 5,

FIG. 8 is a front view of the output shaft,

FIG. 9 is a longitudinal section, in the left hand part of the figure,of the input part of the gear in an assembled state, and in the righthand part of the figure of the driving dog and shaft,

FIG. 10 is a plan from above of the driving dog in FIG. 9,

FIG. 11 is a section similar to the one in FIG. 9, but of a secondembodiment of a driving dog in accordance with the present invention,

FIG. 12 depicts the gear according to FIG. 1, in full size and mountedon a motor,

FIG. 13 illustrates an alternative mounting of the output shaft of thedriving dog,

FIG. 14 illustrates a further alternative mounting of the driving dogoutput shaft,

FIG. 15 is a partial longitudinal section of an alternative embodimentof the driving dog,

FIG. 16 depicts another application of a driving dog in accordance withthe invention, with the driving dog itself being in longitudinalsection,

FIG. 17 is a plan from above of the driving dog in FIG. 16,

FIG. 18 is a depiction, similar to the one in FIG. 16, of a simplifiedembodiment of the driving dog in FIGS. 16 and 17,

FIG. 19 is a side view of an alternative embodiment of the driving dogaccording to FIGS. 16 and 17.

The functional principle of a known translation element is illustratedin FIG. 1. A disc 102 is fastened to an output shaft 101. The disc 102has a plurality of axially directed pins 103 on which rollers 104 arejournalled. These rollers 104 roll over the surface of round holes 105in an excentric wheel 106. The excentric wheel 106 has an excentricity ebetween the input and output shafts. The holes 105 have a diameterexceeding that of the rollers 104 by double the excentricity, i.e. 2e.When the excentric wheel rolls over the internally toothed stationarygear wheel 106b, and thereby executes its planetory movement with therotational rate of the input shaft 106a, the rollers 104 journalled onthe pins 103 will each in turn drive the output shaft 101. Thistranslation device has the disadvantages described under (a)-(e) in theintroductory part of the description.

A first embodiment of the driving dog: in accordance with the inventionwill now be described in connection with the application illustrated inFIGS. 3-10, where the driving dog is incorporated in an excentric gear,which includes a cylindrical housing 1 with a stationary gear wheel 2,integral with the housing 1. The stationary gear wheel 2 has internallycut teeth. A plurality of screws 3 are intended for fastening the gearto the end wall of a motor. The excentric gear further includes a firstexcentric means 6 with a counterweight 7, a first ball bearing 8, anexcentric gear wheel 9, a driving dog 10, two pivot pins 11, 12, a bush13, an output shaft 14, a second ball bearing 15, a bearing housing 16,a third ball bearing 17, a washer 18, a shims washer 19 and a circlip20.

FIG. 4 is a front view of the excentric wheel, with its teeth denoted by21. This wheel furthermore has two diametrically opposing openings or"tooth gaps" 22, 23 in its side surface facing towards the driving dog.The wheel also has an outstanding annular ring on the same side surfacefor receiving the first ball bearing 8.

It will be seen from FIGS. 5-7 that the driving dog includes an annularring 25, provided on one side with two lugs or teeth 26, 27, which aresituated diametrically opposite each other and are intended to glidereciprocatingly in the elongate openings 22, 23 in the excentric gearwheel. To ensure freedom from play in this reciprocal gliding movement,each lug is provided with a slit 28, which is most clearly shown in FIG.7. These lugs keep the driving dog a right fit in the opening 22, 23.There are two radial through bores 29, 30 (FIG. 3) in the annular ring25, these bores being situated diametrically opposite each other, andwith the same angular position as the lugs 26, 27 on the annular ring25. The bores 29, 30 are intended to receive the pivot pins 11 and 12.The driving dog 10 has bevelled surfaces 31 and 32 on either side of theannular ring.

At one end surface the output shaft 14 has a flange 33, the radialextension of which is not greater than that the flange 33 isaccommodated inside the annular ring 25 of the driving dog. The flange33 has two diametrically opposed bores 34, 35, in which the pivot pins11 and 12 are urged with a press fit. The driving dog is thus pivotablymounted on the pivot pins 11, 12. As will be seen from FIGS. 3 and 8 theoutput shaft has a central bore 36 at the same end as the flange 33.This bore 36 is intended to accommodate the bush 13. An annular groove37 for the circlip 20 is disposed on the output shaft a distance fromthe flange 33. The driving dog is assembled in the following way: Thepivot pins 11, 12 are first thrust into the bores 29, 30 and furtherinto the bores 34, 35 of the output shaft. The driving dog thus formedappears in the way illustrated in FIGS. 9 and 10.

In spite of the excentric gear wheel having a low rotational rate, itscentre of gravity rotates with the high rotational rate of the inputshaft. In accordance with the present invention, the driving dog 10translates the slow rotation of the excentric gear wheel to the outputshaft, and encroaches on the axial length of the gear substantially onlyby the thickness of the annular ring 25. The lugs 26, 27 of the drivingdog are slit, or optionally made with a tooth configuration, such as tofit into the elongate openings 22, 23 of the excentric gear wheel. Inits turn, the driving dog is mounted on the pivot pins 11, 12, which arefixed in the output shaft flange 33. By this configuration, the drivingdog will execute a pivoting motion about the pivot pins. The centre ofgravity of the driving dog will remain substantially stationary. Thelugs 26, 27 of the driving dog will have a motion in the opening 22, 23partly like a tooth in a tooth gap and partly reciprocating radiallyrelative the excentric wheel. The angle of the pivoting movement causedby this "roll" of the lugs is about ±3° i.e. rather small. The lugs 26,27 have a large working radius, and their ability to take up load can becompared with a gear wheel of a corresponding size and withcorresponding module. A condition for the desired operation of thedriving dog is that the lugs 26, 27 have the greatest possible torsionalstiffness between them. The annular ring 25 should therefore betorstionally stiff. The bevelled parts 31 and 32 on the ring ensure thatit does not engage against the excentric gear wheel or the baringhousing 16 during the pivoting or rolling motion. The removal of metalto form the surfaces 31, 32 also reduces the moment of inertia of thedriving dog about the pivot pins.

A variant of the driving dog is illustrated in FIG. 11. The previoustooth-like lugs 26, 27 have been formed here as short stiff projections118, 119 on the driving dog 10. These projections 118, 119 have holes121a, 121b bored parallel relative the holes for the pins 11, 12. Thepins 123, 124 urged into the excentric gear wheel 9 using a press fitand are disposed for mounting the driving dog 10. This mounting permitsboth a certain rotational movement of about ±2.6° and a linear movementalong the pins 123, 124 of ±0.3 mm which corresponds to the excentricmotion of the gear wheel 9 for the gear size described in the Figure.

When the driving dog 10 is momentarily deflected out about the pins 11,12, the excentric gear wheel 9 will move axially corresponding to thecord height which, with the values given above, will be about 0.005 mm.Since the wheel 9 is glidably mounted, this axial movement is noproblem. When the excentric wheel 9 is mounted in ball bearings, theball bearings should allow this movement. A standard ball bearingnormally has an axial play which is at least two or three times greater.

A still further variant of the driving dog is illustrated in FIG. 15.The previous variants have had a sliding bearing between the driving dogand the excentric gear wheel and output shaft. For larger gears, wherethe greatest possible efficiency is desired, this gliding bearing may bereplaced by a ball bearing. In FIG. 15 the output shaft has a plate 225which is mounted in prestressed ball bearings 226. The driving dog 10 ismounted on this plate 225 with the aid of ball bushes 228a, 228b on thepins 230, 231 which permits the driving dog 10 to pivot a small angle,but does not allow any translatory movement. The excentric gear wheel232 has two pressed-in pins 233, 234 wich are parallel to said pins. Theball bushes 229a, 229b pressed into the driving dog 10 are journalled onthe pins 233, 234 and allow the driving dog 10 to pivot a small angle aswell as allowing the excentric gear wheel 232 to move translatorily inthe direction of said pins 233, 234.

In all variants described in FIGS. 3-10 and 11-15, the driving dog issubjected to torque on loading (braking) the output shaft. The drivingdog must thus be dimensioned so that a sufficiently high torsionalstiffness is obtained about the lugs or pins on the output shaft.

Another application of the driving dog is illustrated in FIG. 16. Theconnection of two shafts, and thereby the translation of a rotationalmovement requires some type of coupling. The task of the coupling is totranslate the movement without play and without introducing bendingforces between the shafts. This is a usual problem in the art of servosystems. For example, an angle transducer is to be connected to a shaft,the angular position of which it is to measure. A load in the form of abending moment on the angle transducer shaft can easily affect itsmeasuring accuracy.

Bellows or diaphragm couplings are often used here. These couplings havelimited torsional stiffness, as well as great axial and/or diametricaldimensions.

The ideal coupling should have the following properties:

(a) It is insensitive to static and dynamic translatory positionalerrors between the shafts in all three coordinate directions.

(b) It is insensitive to static and dynamic angular errors between theshafts in the coordinate directions at right angles to the axialdirection of the rotation which is to be translated.

(c) It provides true angular translation.

(d) It is torsionally stiff.

(e) It comprises two parts. The parts should be able to be assembled oneeach shaft end individually. This facilates assembly and simplifiesservice exchanges, e.g. of the abovementioned angle transducer.

(f) It should have small volume In particular, its axial length shouldbe small,

(g) It should have low cost.

FIG. 16 illustrates an example of the translation of the angularposition from the shaft end 236 of a motor 235 to the shaft end 238 ofan angle transducer 237. Two cylindrical hubs 239, 240 are attached tothe respective shaft ends 236 238. These hubs each have two radiallydirected pins 241, 242, and two journalling pins 243, 244. A sleeve 245is mounted without play on the pins 243, 244. This sleeve 245 has tworadial slots 246, 247 which have a tight fit to the pins 241, 242 whichas depicted in FIG. 17 will eliminate play.

FIG. 17 illustrates the units of FIG. 16 seen from above. The sleeve 245is suitably manufactured in plastics. By utilising the elasticity of theplastics, a local pre-stress round the pins 241, 242 is obtained, andwhich eliminates wear. Alternatively, the pins 241, 242 may have slits248, 249. Dismantling and exchange of the angle transducer isfacilitated without needing to disturb either half of the coupling. Ofcourse, the cylindrical hubs 239, 240 may be made in plastics, andoptionally integrally with the pins 241, 242.

FIG. 18 illustrate a simplification of the coupling according to FIGS.16, 17. The hub 239 and its two pins 241, 242 has been replaced with acylindrical pin 250 which is pressfitted, screwed, glued or otherwisefixed within a transverse hole 251 extending through a shaft 252.

FIG. 19 illustrates a modification of the embodiment shown in FIGS. 16,17. To reduce the radial load on the journals, and to reduce the wearoccurring due to friction between the slots of the sleeve 245 and thepins 241, 242, the torque is transferred by balls 253 rolling inrecesses or grooves 254 in the sleeve 245. Of course, the balls can bealternatively placed in corresponding grooves in the pins 241, 242.

The embodiments described above can be modified in many ways and variedwithin the scope of the inventive concept.

This novel type of translation element, the driving dog, has severaladvantages over previously known and above-mentioned types, namely:

(a) True angle translation. No superposed pulsation is obtained on theoutput shaft.

(b) Torque is taken from the excentric gear wheel at a large radius,with the reaction forces of the load torque being distributed equally ondiametrically opposed sides of the centre of the output shaft, resultingin that the forces balance each other and do not load the mounting ofthe output shaft. (The frictional force between the driving dog and theexcentric gear wheel loads this mounting however).

(c) The gear is given a very short structural length.

(d) A low price. No tight tolerances. The holes in the driving dog andexcentric gear wheel for the pins are broached with conventional tools.No part matching work is required during assembly.

I claim:
 1. Motion transmitting element, a so-called driving dog ortransmitter, for translating the rotation of the center of gravity of anexcentrically mounted excentric gear wheel (9) to a first shaft (14)while the excentric gear wheel simultaneously executes a planetarymovement about a second shaft, characterized by a rigid body (10, 25)mounted for pivoting about first pivot pins (11, 12) which are disposedsubstantially at right angles to said first shaft (14) said rigid bodyhaving in its symmetry plane for the first pins and first shaft axiallydirected, tooth-like projections (26, 27; 118, 119) which fit withnegligible play into two radially counter-directed apertures (22, 23) inthe excentric gear wheel (9) for allowing said projections to executeradial sliding reciprocatory motion in the apertures simultaneously asthey execute a rolling movement therein, and the rigid body pivots roundthe first pins.
 2. Motion transmitting element as claimed in claim 1,characterized in that the tooth-like projections are replaced withprojections having through openings (121a, 121b) in which two secondpins (123, 124) arranged radially counter-directed in the excentric gearwheel (9) are mounted for allowing the projections to carry out aradial, sliding reciprocatory motion along the second pinssimultaneously as they pivot about them and simultaneously as the rigidbody pivots about the first pins.
 3. Motion transmitting element asclaimed in claim 2, characterized in that the first and second pins aremounted in spherical bushings.
 4. Motion transmitting element fortranslating the rotation of a first shaft to a second shaft, said shaftsnot needing to be co-axial, parallel or needing to have constant mutual,axial spacing, characterized by a sleeve (245), one end of which ispivotably mounted in first pins (243, 244) which are radiallycounter-directed and arranged on one of said shafts, and in the otherend of said sleeve there being arranged slots diametrically oppositeeach other in line with the first pins, there also being second pinsarranged radially opposing on the other of said shafts and intended forbeing in forcetransmitting engagement with the slot.
 5. Motiontransmitting element as claimed in claim 1, characterized by slits (28)being made in the projections for prestressing the projections in theapertures.
 6. Motion transmitting element as claimed in claim 4,characterized in that slits (248, 249) are made in the second pins (241,242) for counter-acting wear between sleeve (245) and said pins. 7.Motion transmitting element as claimed in claim 4, characterized in thatgrooves (254) are made in the sleeve (245) or in the pins (241, 242) forballs (253), the task of which is to transmit the torque andsimultaneously reduce the friction, and thereby the radial and axialforces on the mountings of the shafts.
 8. Motion transmitting element asclaimed in claim 6, characterized in that grooves (254) are made in thesleeve (245) or in the pins (241,242) for balls )253), the task of whichis to transmit the torque and simultaneously reduce the friction, andthereby the radial and axial forces on the mountings of the shafts.